Polypropylene resin is widely used in various types of molded products such as films, sheets and structural components because it is not only excellent in mold processability, heat resistance, mechanical properties and the like, but also has advantages such as having a low specific gravity and being light. Also, in automobile applications and the like in which a reduction in the cost of shipping products and an improvement in fuel efficiency are required, there is a demand for a lighter synthetic resin molded product. The polypropylene resin is flammable, and it is thus necessary to blend a flame retarder in order to impart flame retardancy.
As the flame retarder, an intumescent flame retarder has an excellent flame retardancy. The intumescent flame retarder is composed mainly of polyphosphoric acid, pyrophosphoric acid and a salt of a nitrogen-containing compound, and provides flame retardancy by forming a surface intumescent layer when it is burnt to as to suppress diffusion of decomposed products and heat transfer. Such an intumescent flame retarder is disclosed in, for example, Patent Literature 1. However, a flame-retardant synthetic resin composition disclosed in Patent Literature 1 contains a fluorine-based anti-dripping agent, and for this reason, there is a possibility that the physical properties that are inherent to resin may be impaired.
Even if the fluorine-based anti-dripping agent is not used, there is a problem in that the physical properties that are inherent to resin are impaired if the flame retarder is contained in a large amount. Furthermore, the mass of the resin composition as a whole increases, which is not preferable from the viewpoint of saving energy. Accordingly, there is a demand for a light resin composition with a small amount of a flame retarder.